Ab initio MO computation of the hydration effect on the ionization potential of sodium pyrenesulfonate

STO-3G calculations regarding NaPSA (sodium pyrenesulfonate) with water molecules, NaPSA·(H2O)n, n=0-6, were carried out. Optimizations of the structural variables of water molecules and the distance between Na and S atoms in the -SO3Na function in NaPSA brought about almost no change in the ionization potential from that of pyrene. When the Na atom in the -SO3Na function was separated from the -SO3 function in the case of n=1-3, the ionization potentials became small and were close to that of -SO3− substituted pyrene. In contrast, in the case of n=4, the ionization potential first decreased with increases in the distance between the Na atom and S atom, and then in the range of the distance above 9.5 Å it increased and was again close to that of pyrene. The configurations of water molecules, the electronic structures of HOMOs, and the charge densities are also discussed herein, with it being concluded that the ionization potential of NaPSA is almost the same as that of pyrene, as H3O+ in water solvent always exists near the -SO3 function.